The invention relates to a control valve for a device for variable setting of the control times of gas exchange valves of an internal combustion engine, in particular, according to the preamble of claim 1.
In internal combustion engines, camshafts are used for activating the gas exchange valves. Camshafts are applied in the internal combustion engine in such a way that cams on the camshafts contact cam followers, for example, cup tappets, rocker arms, or valve lifters. If a camshaft is set in rotation, then the cams roll on the cam followers that activate, in turn, the gas exchange valves. Through the position and the shape of the cams, both the opening period and also the opening amplitude, as well as the opening and closing times of the gas exchange valves are set. During the activation of the gas exchange valves, the valve springs exert a force on the cams of the camshaft, by which alternating moments act on the camshaft.
Modern engine designs go so far as to construct the valve drive with a variable design. On one hand, the valve stroke and valve opening period should be able to have a variable construction up until the complete shutdown of individual cylinders. For this purpose, designs such as switchable cam followers or electrohydraulic or electrical valve actuators are provided. Furthermore, it has been shown to be advantageous to be able to influence the opening and closing times of the gas exchange valves during the operation of the internal combustion engine. Here, it is especially desirable to be able to influence the opening or closing times of the intake or exhaust valves separately, in order to set, for example, a defined valve overlap in a targeted way. By setting the opening or closing times of the gas exchange valves as a function of the current characteristic map region of the engine, for example, the current rotational speed or the current load, the specific fuel consumption can be reduced, the exhaust gas behavior can be positively influenced, and the engine efficiency, the maximum torque, and the maximum output can be increased.
The described variability of the gas exchange valve control times is achieved through a relative change in the phase position of the camshaft to the crankshaft. Here, the camshaft is usually in driven connection with the crankshaft via a chain, belt, gear drive or similar acting drive designs. Between the chain, belt, or gear drive driven by the crankshaft and the camshaft there is a device for the variable setting of the control times of gas exchange valves of an internal combustion engine, also called camshaft adjuster below, which transmits the torque from the crankshaft to the camshaft. Here, this device is constructed so that, during the operation of the internal combustion engine, the phase position between the crankshaft and camshaft is reliably maintained and, if desired, the camshaft can be rotated in a certain angular range relative to the crankshaft.
In internal combustion engines with separate camshafts for the intake and exhaust valves, these can each be equipped with a camshaft adjuster. Therefore, the opening and closing times of the intake and exhaust gas exchange valves can be shifted in time relative to each other and the valve overlap can be set in a targeted way.
The seat of modern camshaft adjusters is usually located on the drive-side end of the camshaft. The camshaft adjuster, however, can also be arranged on an intermediate shaft, a non-rotating component, or the crankshaft. It is made from drive wheel driven by the crankshaft and holding a fixed phase relationship relative to the crankshaft, a driven element in drive connection with the camshaft, and an adjustment mechanism transmitting the torque from the drive wheel to the driven element. The drive wheel can be constructed in the case of a camshaft adjuster not arranged on the crankshaft as a chain, belt, or gear wheel and is driven by a chain, belt, or gear drive from the crankshaft. The adjustment mechanism can be operated electrically, hydraulically, or pneumatically.
Two preferred embodiments of hydraulically adjustable camshaft adjusters represent the so-called axial piston adjuster and the rotary piston adjuster.
For the axial piston adjusters, the drive wheel is in connection with a piston and this is in connection with the driven element via helical gearing. The piston separates a hollow space formed by the driven element and the drive wheel into two pressure chambers arranged axial to each other. Now, if one pressure chamber is charged with pressurized medium, while the other pressure chamber is connected to a tank, then the piston shifts in the axial direction. The axial shift of the piston is converted by the helical gearing into a relative rotation of the drive wheel to the driven element and thus the camshaft to the crankshaft.
The so-called rotary piston adjusters are a second embodiment of the hydraulic camshaft adjuster. In this embodiment, the drive wheel is locked in rotation with a stator. The stator and the driven element (rotor) are arranged concentric to each other, wherein the rotor is connected with a non-positive fit, a positive fit, or material fit, for example, by an interference fit, a screw connection, or a weld connection to a camshaft, an extension of the camshaft, or an intermediate shaft. In the stator, several recesses spaced in the peripheral direction are formed that extend radially outward starting from the rotor. The recesses are limited in a pressure-tight manner in the axial direction by a side cover. In each of these recesses, a vane connected to the rotor extends, by which each recess is divided into two pressure chambers. Therefore, two groups of pressure chambers are formed. Through the targeted connection of a group of pressure chambers with a pressurized medium pump and the other group of pressure chambers with a tank, the phase of the camshaft relative to the crankshaft can be set or maintained. The vanes can be constructed, for example, in one piece with the rotor or as separate components that are arranged in an axial vane groove on the outer lateral surface of the rotor and can be forced radially outward by a spring element.
For controlling the camshaft adjuster, sensors detect the characteristic data of the engine, such as, for example, the current phase position of the camshaft relative to the crankshaft, the load state, and the rotational speed. This data is fed to an electronic control unit that, after comparison of the data with a characteristic data map of the internal combustion engine, controls the inflow and outflow of pressurized medium to the different pressure chambers.
In order to adjust the phase position of the camshaft relative to the crankshaft, in hydraulic camshaft adjusters one of the two counteracting pressure chambers is connected to a pressurized medium pump and the other is connected to the tank. The supply of pressurized medium to one chamber in connection with the discharge of pressurized medium from the other chamber shifts the piston/vane separating the pressure chambers, by which the camshaft is rotated relative to the crankshaft in axial piston adjusters by an axial shift of the piston by the helical gearing. In rotary piston adjusters, through the pressurization of one group of pressure chambers and the depressurization of the other group of pressure chambers, the vane is shifted in the peripheral direction and thus directly rotates the camshaft relative to the crankshaft. In order to maintain the phase position, both pressure chambers are either connected to the pressurized medium pump or both are separated from the pressurized medium pump and also from the tank.
The control of the pressurized medium flows to or from the pressure chambers is realized by a control valve, usually a 4/3 proportional valve. This is made essentially from a hollow cylindrical valve housing, a control piston, and an adjustment unit. The valve housing is provided with a connection for each group of similarly acting pressure chambers (working connection), a connection for the pressurized medium pump, and at least one connection to a tank. These connections are usually constructed as annular grooves on the outer lateral surface of the valve housing that communicate via radial openings with the interior of the control piston. With the valve housing, the control piston is arranged so that it can move in the axial direction. The control piston can be positioned by a control unit that is usually activated electromagnetically or hydraulically against the spring force of a spring element in the axial direction into any position between two defined end positions. The outer lateral surface of the control piston is essentially adapted to the inner diameter of the valve housing and provided with annular grooves and control edges. By controlling the control unit, the individual connections can be connected to each other hydraulically, by which the individual pressure chambers can be connected selectively to the pressurized medium pump or the tank. Likewise, a position of the control piston can be provided in which the pressurized medium chambers are separated both from the pressurized medium pump and also from the pressurized medium tank.
Such a control valve is known from JP 07-229408A. In this case, five annular grooves spaced in the axial direction relative to each other are formed on the outer lateral surface of the valve housing, wherein each of the annular grooves is used as a connection of the valve. In each groove base of the annular grooves, a radial opening is formed that opens into the interior of the valve housing. Here, openings of adjacent groove bases are offset in the peripheral direction by 180° relative to each other. Within the valve housing, a solid control piston is arranged that can be positioned by an electromagnetic control unit between two end stops against the force of a spring within the valve housing in the axial direction. The outer diameter of the control piston is adapted to the inner diameter of the valve housing. In addition, on the control pistons three annular grooves are formed by which adjacent connections can be connected to each other as a function of the position of the control piston relative to the valve housing.
From DE 198 53 670 A1, another embodiment of such a control valve is known. This differs from the embodiment shown in JP 07-229408A in that the control piston has a hollow construction. In addition, on the outer lateral surface of the valve housing there are only three connections, wherein a fourth connection is formed in the axial direction of the valve housing. Pressurized medium can now be led via the axial supply connection, according to the position of the control piston relative to the valve housing, to one of the two working connections. Simultaneously, the other working connection is connected to the tank connection by an annular groove formed on the outer lateral surface of the control piston. In this embodiment of a control valve, the position of the supply connection and the tank connection is exchangeable.
Through the rolling of the cams of a camshaft on the cam follower of a valve drive, periodic alternating moments act on the camshaft. These alternating moments are transmitted to the rotor of the camshaft adjuster, by which pressure spikes are produced in the pressure chambers. In order to prevent these pressure spikes from being transmitted via pressurized medium lines and the control valve into the pressurized medium circuit of the internal combustion engine, check valves are provided between the control valve and the pressurized medium pump. Here, check valves that are separate or integrated in the control valve are provided.
A check valve integrated in the control valve is shown, for example, in EP 1 291 563 A2. In this embodiment, within an annular groove formed on a valve housing there is a closing element made from a strip bent into a ring. The annular groove is defined in the radial direction by a sleeve. Both in the sleeve and also in the groove base of the annular groove there are openings by which the pressurized medium can reach into the interior of the valve housing. In addition, the strip is made from an elastic steel and is biased outward in the radial direction. If the pressure in the interior of the valve housing exceeds the pressure of the pressurized medium arriving at the opening of the sleeve, then the strip contacts the inner lateral surface of the sleeve and thus prevents the pressurized medium flow from the interior of the valve housing to the opening of the sleeve. Conversely, the strip is deformed inward by the pressurized medium arriving at the opening of the sleeve, by means of which pressurized medium can lead from the opening of the sleeve into the interior of the valve housing.
The invention is based on the objective of providing an alternative construction of a control valve for a camshaft adjuster with an integrated check valve.